A more thorough explanation:

A MULTO FORTIORI

A multo fortiori is a Latin phrase that means "by far the stronger reason." It is often used to emphasize a point or argument that is even more valid than a previous one. It is similar to the phrase "a fortiori."

• If John can run a mile in under 5 minutes, a multo fortiori he can run a mile in under 6 minutes.
• If a doctor recommends a patient to quit smoking for their health, a multo fortiori they should quit if they have a family history of lung cancer.

In the first example, the argument is that if John can run a mile in under 5 minutes, it is even more certain that he can run a mile in under 6 minutes. The second example shows that if a doctor recommends quitting smoking for one reason, it is even more important to quit if there is a higher risk factor involved.